This invention relates to the treatment of aprotic solvents. In one of its aspects this invention relates to the removal of acidic compounds from aprotic solvents. In still another of its aspects this invention relates particularly to the treatment of N-methyl-2-pyrrolidone for the removal of phenol and other acidic compounds.
In processes for the recovery of N-methyl-2-pyrrolidone (NMP) which is used in the production of poly(phenylene sulfide) the recovery is usually effected by employing fractionation columns in series. Into the first column is fed a combination of materials which results from the poly(phenylene sulfide) production process which has N-methyl-2-pyrrolidone as the major constituent with water, dichlorobenzene, light materials, and various acidic materials such as phenol, N-methylsuccinimide, dimethylpyrrolidone as impurities. The first fractionation column is operated at conditions to remove the water, dichlorobenzene, and other materials lighter than the NMP. Acidic contaminants are not completely removed in the operation of this fractionator.
It is desirable, however, to keep acidic impurities in NMP that is used for poly(phenylene sulfide) production to a minimum since their presence, particularly phenol and N-methylsuccinimide, can upset the stoichiometry of the reaction and result in the formation of polymer that is off-specification. Under usual operating conditions further fractionation of the kettle product from the first fractionation column will produce NMP overhead which still contains acidic impurities at a level above the minimum desired. By the process of this invention a method is provided by which kettle liquid and/or overhead product from the fractionation columns can be treated for the removal of acidic contaminants thereby reducing the amount of material that must be discarded or retreated.
N-methyl-2-pyrrolidone is typical of aprotic solvents and the purification of this material is also typical of the purification processes for other aprotic solvents. The invention exemplified herein is applicable to the removal of acidic contaminants from aprotic solvents in general.
It is therefore an object of this invention to provide a method for removing acidic contaminants from aprotic solvents. It is still another object of this invention to provide a method for removing acidic contaminants associated with N-methyl-2-pyrrolidone recovered from use in the production of poly(phenylene sulfide). It is still another object of this invention to facilitate the recovery of N-methyl-2-pyrrolidone from a poly(phenylene sulfide) production that can be recycled for further production of poly(phenylene sulfide).
Other aspects, objects and advantages of this invention will become apparent upon study of this specification, the drawings and the appended claims.